Inorganic 6: Reactions of Aqueous Ions

Question 1

What are aqua ions?

Answer 1

Complexes formed when a salt of a transition metal is dissolved in water
Water molecules cluster around Fe2+ ions, creating an octahedral complex
Water molecules use one of their lone pairs to form a co-ordinate bond to the metal ion

Question 2

Why are solutions of Fe3+ acidic, when Fe2+ solutions are not?

Answer 2

Fe3+ is smaller and more highly charged, so has a higher charge density
Making it more strongly polarising
So the iron strongly attracts electrons from the oxygen atoms of water
Weakening the O-H bond
Releasing a H+ ion, which makes the solution acidic

Question 3

What are hydrolysis reactions?

Answer 3

Reactions of transition metal complex ions with water
Water receives a proton, so acts as a Bronsted-Lowry base, and the complex ion as a Bronsted-Lowry acid

Question 4

What is a Lewis acid?

Answer 4

An electron pair acceptor in the context of co-ordinate bonds

Question 5

What is a Lewis base?

Answer 5

An electron pair donor in the context of co-ordinate bonds
A ligand is a Lewis base

Question 6

What colour is [Fe(H2O)6]2+?

Answer 6

Green solution

Question 7

What colour is [Cu(H2O)6]2+?

Answer 7

Blue solution

Question 8

What colour is [Fe(H2O)6]3+?

Answer 8

Yellow/brown in solution
Violet is seen in solid hydrated salts

Question 9

What colour is [Al(H2O)6]3+?

Answer 9

Colourless solution
Because Al3+ has a full outer orbital

Question 10

Write an equation for the equilibrium that happens in aqueous solutions of metal aqua ions (2+).

Answer 10

[M(H2O)6]2+ + H2O –> [M(H2O)5(OH)]+ + H3O+

Question 11

What colour is Fe(OH)2(H2O)4?

Answer 11

Green precipitate

Question 12

What colour is Cu(OH)2(H2O)4?

Answer 12

Blue precipitate

Question 13

What colour is Fe(OH)3(H2O)3?

Answer 13

Brown precipitate

Question 14

What colour is Al(OH)3(H2O)3?

Answer 14

White precipitate

Question 15

Write an equation for a deprotonation reaction of [Al(H2O)6]3+ with limited hydroxide ions/ ammonia.

Answer 15

[Al(H2O)6]3+ + OH-(aq) –> [Al(H2O)5(OH)]2+ + H2O(l)

[Al(H2O)5(OH)]2+ + OH-(aq) –> [Al(H2O)4(OH)2]+ + H2O(l)

[Al(H2O)4(OH)2]+ + OH-(aq) –> [Al(H2O)3(OH)3 + H2O(l)

Question 16

Describe the reactions of aluminium hydroxide Al(H2O)3(OH)3 with excess OH- and excess H+.

Answer 16

Al(H2O)3(OH)3 + OH- –> [Al(OH)4]- + 3H2O (l)

Al(H2O)3(OH)3 + 3H+ –> [Al(H2O)6]3+-

Question 17

Describe the reaction of excess NH3 with Cu(OH)2(H2O)4.

Answer 17

Cu(OH)2(H2O)4 + 4NH3 –> [Cu(NH3)4(H2O)2]2+ + 2H2O + 2OH-
Incomplete substitution

Question 18

What colour is [Cu(NH3)4(H2O)2]2+?

Answer 18

Deep blue solution

Question 19

What does amphoteric mean?

Answer 19

Acts as both acid and base

Question 20

Describe the reaction of hexaaquacopper(II) with carbonate solution.

Answer 20

[Cu(H2O)6]2+ + CO32- –> CuCO3 + 6H2O
This is a precipitation reaction, where blue/green CuCO3 precipitate forms

Question 21

Describe the reaction of hexaaquairon(II) with carbonate solution.

Answer 21

[Fe(H2O)6]2+ + CO32- –> FeCO3 + 6H2O
This is a precipitation reaction, where a green precipitate of FeCO3 forms

Question 22

Describe the reaction of hexaaquairon(III) with carbonate solution.

Answer 22

2[Fe(H2O)6]3+ + 3CO32- –> 2Fe(OH)3(H2O)3 + 3CO2 + 3H2O

Fe(OH)3(H2O)3 is a brown precipitate

Question 23

Describe the reaction of hexaaquaaluminium(III) with carbonate solution.

Answer 23

2[Al(H2O)6]3+ + 3CO32—> 2Al(OH)3(H2O)3 + 3CO2 + 3H2O

Al(OH)3(H2O)3 is a white precipitate

Question 24

Summary for reactions of 2+ complex ions.

Answer 24

Question 25

Summary for reactions of 3+ complex ions.

Answer 25